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Determine The Speed of a Charge at a given point

  1. Feb 9, 2015 #1
    1. The problem statement, all variables and given/known data
    Given: The electric potential function: V= 3x^2 + 2xy +(y^2)z + 20
    a) A 4 coulombs, 2kg charge is released from the origin. Determine the speed of the charge at (1,1,-1)

    2. Relevant equations
    Kinetic Energy= 1/2 mv^2

    3. The attempt at a solution
    I tried to use the fact that the change in potential energy is equal to the negative change in kinetic energy.
    I calculated the change in electric potential to be 4 V and set that equal to the negative change in kinetic energy, which would just be -1/2 mv^2
    However, when I solve for the velocity, I get the square root of negative 4. Have I done something wrong or is the problem just flawed?
  2. jcsd
  3. Feb 9, 2015 #2


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    Homework Helper
    Gold Member

    I think you're right. The question is flawed. A positive charge will not go from lower to higher potential without some external force.
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